1. Field of the Invention
The present invention relates to a thin-film magnetic head incorporating at least an induction-type electromagnetic transducer and a method of manufacturing such a thin-film magnetic head, and to a head gimbal assembly including a thin-film magnetic head, and a hard disk drive.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as a real recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading.
A write head comprises: a bottom pole layer and a top pole layer including magnetic pole portions opposed to each other and located in a region on a side of a medium facing surface, that is, a surface facing toward a recording medium; a write gap layer provided between the pole portion of the bottom pole layer and the pole portion of the top pole layer; and a thin-film coil at least part of which is disposed between the bottom and top pole layers and insulated from the bottom and top pole layers.
To enhance the recording density of the write head, it is particularly required to reduce the pole width that defines the write track width and to improve writing characteristics. However, if the pole width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are reduced. Consequently, the smaller the pole width, the greater improvements in writing characteristics are required. To enhance the recording density of the write head, it is also required to suppress ‘side erase’ that is a phenomenon in which, when data is written on a specific track, data contained on an adjacent track is erased.
Thin-film magnetic heads are manufactured through semiconductor producing techniques. Therefore, a plurality of thin-film magnetic heads are manufactured at one time out of a single wafer. If an effective write track width is reduced down to 0.3 μm or smaller, for example, it is difficult to reduce variations in pole width of the thin-film magnetic heads manufactured out of the single wafer.
As disclosed in the Published Unexamined Japanese Patent Application Heisei 11-353616 (1999) and the U.S. Pat. No. 6,043,959, for example, one of the techniques known for manufacturing a thin-film magnetic head having a reduced pole width is to divide the top pole layer into a pole portion layer that defines the pole width and a yoke portion layer having a greater width. Another technique for manufacturing a thin-film magnetic head having a reduced pole width is a technique for trimming the pole portion as disclosed in the Published Unexamined Japanese Patent Application Heisei 11-353616 and the U.S. Pat. No. 6,043,959, too. This technique is to etch the write gap layer and at least a portion of the pole portion of the bottom pole layer close to the write gap layer, using the pole portion of the top pole layer as a mask, and to thereby align the sidewalls of the pole portion of the top pole layer, the write gap layer and at least the portion of the pole portion of the bottom pole layer. Dry etching is used for this etching.
Still another technique for manufacturing a thin-film magnetic head having a reduced pole width is to make the pole portion of the bottom pole layer, the write gap layer and the pole portion of the top pole layer have the same plane geometries as disclosed in the Published Unexamined Japanese Patent Application Heisei 6-28626 (1994) and the Published Unexamined Japanese Patent Application Heisei 6-314413 (1994). Through this technique, the pole portion of the bottom pole layer, the write gap layer and the pole portion of the top pole layer may be consecutively formed by plating through the use of a single photoresist frame.
A technique disclosed in the Published Unexamined Japanese Patent Application 2001-118214 is to form an insulating layer for defining the throat height on the layer underlying the bottom pole layer and then form a photoresist frame, and to form the pole portion of the bottom pole layer, the write gap layer and the pole portion of the top pole layer by plating through the use of the photoresist frame. The throat height is the length (height) from the medium facing surface to the point at which the space between the two pole layers starts to be created.
To control the pole width by using the technique for trimming the pole portion as disclosed in the Published Unexamined Japanese Patent Application Heisei 11-353616 and the U.S. Pat. No. 6,043,959, the pole width is controlled by dry etching. Therefore, there arises a problem in this case that variations in pole width of a plurality of thin-film magnetic heads manufactured out of a single wafer are increased.
In contrast, as disclosed in the Published Unexamined Japanese Patent Application Heisei 6-28626 and the Published Unexamined Japanese Patent Application Heisei 6-314413, to form the pole portion of the bottom pole layer, the write gap layer and the pole portion of the top pole layer through the use of a single photoresist frame, the pole width is controlled by photolithography. In this case, variations in pole width of a plurality of thin-film magnetic heads manufactured out of a single wafer are made smaller, compared to the case in which the pole width is controlled by dry etching. If the photoresist frame is formed on a flat surface, the frame is formed with accuracy. As a result, if the pole portion of the bottom pole layer, the write gap layer and the pole portion of the top pole layer are formed through the use of the photoresist frame formed on the flat surface, variations in pole width are made much smaller.
According to the thin-film magnetic head manufactured through the techniques disclosed in the Published Unexamined Japanese Patent Application Heisei 6-28626 and the Published Unexamined Japanese Patent Application Heisei 6-314413, the throat height is equal to the distance between an end located in the medium facing surface and the other end of the aggregate of the pole portion layer of the bottom pole layer, the write gap layer, and the pole portion layer of the top pole layer. Consequently, according to this thin-film magnetic head, if this distance is long, the throat height is great, too. As a result, it may be impossible to generate a magnetic field sufficient for writing from the medium facing surface. On the other hand, if the above-mentioned distance is short, the area in which the pole portion layer and the yoke portion layer of each of the top and bottom pole layers are in contact with each other is reduced. As a result, it is impossible to supply a sufficient magnetic flux from the yoke portion layers to the pole portion layers. Consequently, it may also be impossible to generate a magnetic field sufficient for writing from the medium facing surface.
If the technique disclosed in the Published Unexamined Japanese Patent Application 2001-118214 is used, the area in which the pole portion layer and the yoke portion layer of the top pole layer are in contact with each other is increased while the throat height is reduced. Through this technique, however, the photoresist frame is not formed on a flat surface but formed on a surface having a difference in level created by the insulating layer for defining the throat height. As a result, it is difficult to form the photoresist frame with accuracy. Therefore, this technique has a problem that it is difficult to reduce variations in pole width when the pole width is reduced down to 0.3 μm or smaller, for example.